Secure content pre-distribution to designated systems

Described is a technology by which encrypted content is pre-distributed to recipients during a pre-distribution timeframe, for example to distribute protected content to many clients in a controlled manner. At a release moment, a key for decrypting the encrypted content is released. For example, a software update may be pre-distributed in this manner, whereby many clients may receive the updates over time but the update cannot be analyzed for hacking purposes, e.g., to use the update to figure out a prior vulnerability. By rapidly and widely disseminating the key at the release moment, the update is installed on a large percentage of client systems before those systems can be exploited. The content may be allowed to expire before the key is released, or may be canceled or replaced. The content may include a complete file, and/or a delta file that changes another file into a resultant piece of content.